Plant profiles  -  Todea

Family : Osmundaceae

I've got a bit of a thing for ferns that can grow in full sun. Throw in the ability to withstand dry or seasonally waterlogged conditions, endure toxic soils and attain a growth form not unlike a cycad, and I'll buy it a drink at the bar. Yet, despite all of its virtues, this glorious brute of a fern has barely registered on the radar of gardeners or the landscape industry in NZ.

Aside from a lack of knowledge about its general existence, this is probably due to its slow growth as a sporeling (nurseries don't like to wait too long for a saleable plant), the narrow window for sourcing viable spores for propagation, and the effect that thrips can sometimes have on plants growing in certain positions (notably sheltered locations in shade).

Returning to its cycad-like growth form, this impressive fern can play a similar role to para (Ptisana salicina, also known as king fern), as substantial structural elements within plantings in high light (as proven by a large specimen growing out in the open by Oratia Native Plant Nursery's main sales area for decades) or open woodland. The image above shows the kind of growing station in which Todea barbara is often found (within its extant populations in New Zealand); punching up through tangle fern (Gleichenia) in infertile gumland habitats.

There are just two members of the genus, with our native species also occurring in southern Africa and southeastern Australia, whilst the other species, T. papuana, is found in New Guinea. The genus belongs to a particularly ancient family of ferns, the Osmundaceae. Its credentials are only reinforced in this respect (even if only coincidentally) by its presence in the understorey of the tiny remaining areas of forest containing Wollemi Pine (Wollemia nobilis) in New South Wales.

Todea barbara
Royal fern; King fern

The respective merits of botanical names and common names are often commented upon, with a regular refrain being that it would be much simpler for non-specialists if common names were deployed. Although the reasons for having just one, universally-recognised system (to which botanical names conform) is not up for genuine debate, its practical value is demonstrated very well by Todea barbara. If we were to prefer one of its common names, 'royal fern', there would be a real risk of planting a pernicious exotic weed in its stead (Osmunda regalis), whilst another of Todea's names, 'king fern', would cause confusion between this species and a very different native fern, Ptisana (syn. Marattia) salicina.

With that disclaimer out of the way (to explain why neither of the aforementioned common names will appear herein), the images below show this species' ability to grow within a wide range of situations, from relatively dry, exposed banks to seasonally waterlogged gumland. Although it is capable of inhabiting very shaded areas (in which the species attains its largest dimensions), this is normally 'open shade', in which the sub-canopy is much clearer than within dense forest.

One of the most intriguing habitats in which Todea barbara occurs is on toxic soils (overlying serpentinite) at Hikurua / de Surville Cliffs (North Cape). In these soils, very high concentrations of minerals (notably iron and magnesium) create conditions that exclude many species and plant communities, as well as setting up the basis for the evolution of new species.

Todea's ability to grow in open places like coastal cliffs carries through to its cultivation, as mentioned in the opening stanza of this plant profile. In our own plantings, we have grown it in full sun (including through the driest summer on record in Auckland), with most specimens retaining foliage throughout, and any plants on which fronds dried up in the extreme conditions resprouting at the beginning of autumn.


Similar to survival strategies employed by cycads, para (Ptisana salicina), or flowering bulbs, Todea barbara's resilience is partially enabled by the presence of a swollen base (termed a caudex), to which growth can retreat in the most challenging periods. With considerable age, the caudex develops into trunks1 (formed, like other trunking ferns, from densely-packed roots) that can attain massive dimensions - with one early author on the subject citing the presence of ancient specimens in Australia with trunks weighing one and a half tonnes2.

 


Footnotes

  1. Although technically, any trunk on ferns or monocotyledonous plants may be described as a 'caudex', the term is commonly applied more towards the swollen base of such plants prior to forming trunks.
  2. The acccount mentioned here is from H. B. Dobbie's book, 'New Zealand Ferns' (3rd Ed.; 1930; Whitcombe & Tombs).